Synthesis of a stable adduct of dialane(4) (Al₂H₄) via hydrogenation of a magnesium(I) dimer

The desorption of dihydrogen from magnesium(II) hydride, MgH₂ (containing 7.6 wt% H), is reversible. MgH₂ therefore holds promise as a hydrogen storage material in devices powered by fuel cells. We believed that dimeric magnesium(I) dimers (LMgMgL, L =β-diketiminate) could find use as soluble models to aid the study of the mechanisms and/or kinetics of the hydrogenation of magnesium and its alloys. Here, we show that LMgMgL can be readily hydrogenated to yield LMg(μ-H)₂ MgL by treatment with aluminium(III) hydride complexes. In one case, hydrogenation was reversed by treating LMg(μ-H)₂ MgL with potassium metal. The hydrogenation by-products are the first thermally stable, neutral aluminium(II) hydride complexes to be produced, one of which, [{(IPr)(H)₂ Al}₂] (IPr =:C[{(C₆H₃-i-Pr₂-2,6)NCH}₂]), is an N-heterocyclic carbene adduct of the elusive parent dialane(4) (Al ₂H₄). A computational analysis of this compound is presented.